1. Field of the Invention
The present invention relates to an electronic musical instrument for electronically generating a musical tone waveshape.
2. Description of the Prior Art
An electronic musical instrument of a waveshape reading out system which employs a waveshape memory storing a musical sound waveshape either in the analog form or in the digital form, and is operative so that the stored contents are repetitively read out at a given rate of time from said waveshape memory to thereby form a musical tone waveshape, is disclosed in, for example, U.S. Pat. No. 3,515,792 Specification (Inventor: Ralph Deutsch; Title: DIGITAL ORGAN).
In an electronic musical instrument, in general, which employs the above-mentioned system, the musical tone waveshape which is read out from the waveshape memory is always constant in amplitude (tone volume) and tone color relative to time. Accordingly, in order to impart the musical tone a variation of amplitude (envelope) with time, the instrument is arranged in general so as to multiply the musical tone waveshape read out from the waveshape memory by an amplitude factor which varies with time. With such a known arrangement, there can be attained a variation of tone volume of the musical tone in accordance with the passage of time. Nevertheless, it is not possible to obtain such a musical sound that its tone color varies with time. In order to attain a variation of tone color with time, it is necessary according to the prior art to further pass the musical sound waveshape read out from the waveshape memory through a complicated variable filter arranged so that its frequency characteristic varies with time.
As stated above, in case it is intended to generate a musical tone which is rich in variation and in expression by the use of an electronic musical instrument employing the known waveshape reading out system, it is necessary to equip this instrument with very complicated and expensive peripheral circuits. Thus, it is quite difficult to obtain, from an electronic musical instrument of a simple structure, such a decaying musical sound as the sound of a piano, a guitar, a harp and a xylophone, whose tone volume exhibits a decay with time and yet is accompanied with variation of tone color.